Lubrication of each of sliding parts of a compressor used in a refrigerator is ensured by a refrigerator oil which is compatible with a refrigerant used. When the sliding parts are made of aluminum and/or iron, however, there has still been a problem of wear and seizing. There has also been caused a problem of capillary clogging due to insufficient sludge dispersibility.
To cope with these problems, Patent Document 1 proposes the use of a refrigerator oil composition containing a base oil of a specific polyether and a phosphorothionate such as an alkyl phosphorothionate or an aryl phosphorothionate.
Patent Document 2 proposes a lubricating oil composition for a sliding part, containing a mineral oil and/or a synthetic oil and, added thereto, 0.05 to 5% by weight of a thiol.
With these proposals, however, it has still been impossible to satisfy both sludge dispersibility and performance of wear and seizure prevention of sliding parts.
In this circumstance there is a demand to establish a refrigerator lubricating system which satisfies both sludge dispersibility and prevention of wear and seizing of a sliding part by improving the refrigerator oil or by improving both the refrigerator oil and the lubricating material.    [Patent Document 1] Japanese Unexamined Patent Publication No. 2000-17282    [Patent Document 2] Japanese Unexamined Patent Publication No. H05-117680